Process of manufacturing asphaltic paving material.



UNITED STATES PATENT OFFICE.

CHARLES N. FORREST, 0F RAHWAY, NEW" JERSEY, ASSIGNOR TO THE BARBER ASPHALT PAVING COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPO- RATION OF WEST VIRGINIA.

PROCESS OF MANUFACTURING ASPHALTIC PAVING MATERIAL.

No Drawing.

To all whom it may concern:

Be it known that I, CHARLES N. FORREST, a citizen of the United States, residing at Rahway, in the county of Union and State of New Jersey, have invented a certain new and useful Process of Manufacturing Asphaltic Paving Material, of which the following is a specification.

My invention relates to a process for dehydrating crude natural asphalt with formation of an asphaltic cement, as an incident to its incorporation with a suitable mineral aggregate, so as to form a paving mixture for highway or other pavements suitable for motor, horse-drawn or other vehicles.

Asphalt pavements consist of the comb1- nation of an asphaltic cementing medium with a suitable mineral aggregate. When natural asphalt such as that from the island of Trinidad, B. W. I.', known as lake or land Trinidad asphalt, or from Venezuela, known as Bermudez asphalt, is employed as the cementing material of a pavement containing also either sand or crushed stone or both, it has heretofore been the practice to first dehydrate the crude natural asphalt by heating it in tanks or stills, by means of either direct fire under the tanks or steam coils inside of the same, to a temperature of approximately 325 F. The dehydrated asphalt prepared thus or in any other way is a relatively hard substance, too hard for direct use in a bituminous pavement mixture. It is therefore softened to a suitable consistency in afire or steam heated kettle, by adding approximately 20 parts by weight of a heavy petroleum oil to one hundred parts of the dehydrated or so-called refined natural asphalt, after which it is drawn from, the,

fluxing tank in suitable quantities and at convenient times for preparing the paving mixture in conjunction with a hot mineral aggregate. Accordingly the operations customarily employed in the manufacture of asphaltic paving material involve, first, dehydrating the crude asphalt by means of heat, second, fluxing the dehydrated asphalt with heavy petroleum oil by means of heat, and third, incorporating the resulting hot fluxed asphalt cement with a hotmineral aggregate,

Specification of Letters Patent. I Application filed January 14, 1910. Serial No. 537,986.

Patented Feb. 10, 1914:.

My invention consists in a process by which all of the functions of the foregoing three separate operations are performed during one general handling of the materials,

and with but one application of heat, and all at the final stage of the operation of preparing by direct composition a suitable paving mixture.

A paving mixture, the mineral aggregate of which consists entirely of sand, (and by sand I mean particles which will pass a wire screen or its equivalent, having eight or ten meshes per lineal inch), contains approximately ten per cent. bitumen and ninety per cent. mineral aggregate. A paving mixture, the mineral aggregate of which is crushed stone, gravel or slag varying 111 size or entirely of one size from two and onehalf inches to eight mesh, will require less than ten per cent. bitumen, the exact amount required depending upon the size, number and shape of said particles of stone in a given volume. In any event the exact amount of bitumen in any pavement mixture, as Well as the consistency of the same, is fixed by experience and suitable simple tests well known in the paving art. Crude Trinidad and crude Bermiidez asphalts contain a substantially constant proportion of water, about 29 to 30% in'either case, and the exact amount of water present is very readily determined by a simple test.

In order to practise my process after having determined the factors set forth in the last paragraph a suitable proportion calculated by weight upon itsbituminous content,

of the crude asphalt of 'either form, is deposited in a pug mill or other suitable mixing device which contains also hot sand, stone or both at a temperature of about 400 F.

The proportions are fixed by a determination. of the percentage of asphalt required for the aggregate and that amount of asphalt is employed making allowance for the contained water. Assuming that the crude asphalt is added at atmospheric temperatures, the mineral aggregate heated and proportioned as above explained, will contain a much larger number of heat units than are required to convert'into steam substantially all of the water carried by the crude asphalt.

The result of operating the pug mill is that the asphalt is agitated and thoroughly mixed with the hot mineral aggregate, and the Water very quickly and thoroughly driven from the same. A cloud of watery vapor arises from the mixer, but in one or two minutes this ceases and indicates that the asphalt has been completely dehydrated. Thereupon a suitable quantity of heavy petroleum oil of proper: quality is added to the mixture'of hot sand and asphalt in the mill and agitated for an additional two minutes or more, thus producing the final mixture in suit-able form for spreading in the customary manner upon a roadway.

As an example of the proper proportions to be used in an instance where it is proposed to employ crude Trinidad asphalt, let it be supposed that'the crude asphalt contains by analysis'the following: i

Water 29.0% Bitumen 39.0% Mineral matter 25.0% Difierence 7.0%

Crude Trinidad asphalt. 18A parts Mineral aggregate 79.0 Heavy petroleum oil 2.6

The result will be that after the dehydration of the crude asphalt and the incorporation of the petroleum oil, the composition of the resulting paving mixture will be approximately 10% bitumen and 90% mineral aggregate.

As an example of the proper proportions to be used in an instance where it is roposed to employ crude Bermudez. asp alt let it be supposed that the Bermridez asphalt contains by analysis the following:

Under such circumstances, the ingredients for a normal sand mineral aggregate should be combined as follows? Crude Bermiidez asphalt 12.7%. Mineral aggregate f.- -l- 85.6% Heavy petroleum oiL 1.7%

. asphalt, whereby tion of the crude asphalt and the incorporation of the petroleum oil, the composition of the resulting paving mixture will be approximately bitumen 10.6%, and mineral aggregate 89.4%.

While the above proportions are typical and are approximately correct for a serviceable mixture, it is to be understood that different sands vary as to their capacity for holding asphalt as also does crushed stone. Likewise a mixture for use in a cold climate may require more petroleum oil than one for use in a warm climate. It will, therefore, be understood that my process is not to be limited to any particular proportions of the materials, butincludes the immediate combination with a hot mineral aggregate, of a suitable proportion of a crude asphalt calculated upon its bituminous content, so that dehydration of, the asphalt is effected by the heat impartedto it during the process of mixing with the hot aggregate, with the result that after dehydration, and the addition of a proper amount of fluxing material, there will remain combined with the aggregate a cementing material of a character and in proportions suitableto the aggregate, with which it is combined, the result being a properly composed paving mixture. It will further be understood that although I propose primarily to utilize the heat of the aggregate for the purpose of etfecting dehydration of the crude asphalt, the heat for this purpose, or part of it, may, if desirable, be obtained from other sources and imparted to the mixture. The distinguishing feature of my process is that the dehydration of the crude asphalt is eiiected as an incident of its mixture with the aggregate with which it is combinedfor making the paving mixture, as distinguished from former processes Where dehydration has been effected at a previous stage of the process, and before the asphalt is mixed with the aggregate.

Having thus described my process, I claim s 1. The process of making a paving mixture which consists in incorporating with crude water containing asphalt, a suitable proportion of a mineral aggregate sufficiently heated to supply the amount of heat required to drive ofi the water from the crude dehydration is eii'ected a;

an incident to the act of incorporation,

' with the result of making a mixture of an and an asphalt cementing meaggregate suitable for a paving dium in proportions mixture.

2. The process of makin an asphaltic pavingmixture, which consists in directly and intimately combining in suitable proportions a hot'mineral aggregate, an amount The result Willbe-thatafterthe dehydral of crude Water containing'asphalt calculated upon its bituminous content, and an oil flux, Intestimony whereof, I have hereunto said mineral aggregate being heated hot signed my, name, at Maurer,,-New Jersey, enough to drive oflf substantially all of the this 12th day of January, 1910. I

water 7 contained by the ,crude asphalt,

whereby the crude asphalt is immediately CHARLES FO deh'ydratedand converted intoan asphaltic -Witnesses: cement, proportioned 'withreference to the .JOHN S. MILLER, J r.,

aggregate to form the paving mixture. MICHAEL P. ENNIS. 

